Variable resistance



A. W. FISCHER VARIABLE RESISTANCE Original Filed Aug. 16 1943 ll lll-Ilill Sept. 10, 1946.

[Hill II II II II II II .llll 3: mm WWW @Zimi M Sc at tomegd Patented Sept. 10, 1946 V ARIABLE RESISTANCE ignor ..'Fischer,.H1ghland Park, Mich ass l ieral Motors Corporation, Detro1t,l\l1ch.,

a corporation of Delaware 'l'No'. l a lic'ation August 16, 1)43, Ser1a fivideii and this application August 92 4 Claims.

This invention relates to variable electrical resistance means and resistance meansin in infinitely small 7 titled Recording mechanism.

The use of resistance in electric circuits whose value can be varied is very wide spread. One of the common forms of Variable resistance'which is used particularly in laboratory or research instruments is the slide wire type in which a length of resistance wire is wound upon a cylinder and fore changes as the contact is moved axially by the value of one complete turn :at a time. This in some instances may .be entirely a too rough a variation to be used "in particularly sensitive recording means or other similar constructions.

It is therefore an object of my invention to With these and other objects in View, which will become apparent as the the accompanying drawing, in which:

Figure 1 is a sectional view through a recording mechanism in which my invention is incorporated.

Figure 2 is an enlarged View partially in section showing the variable resistance of my invention.

Figure 3 is a View similar to Figure 2 showing a modified form of my invention.

As mentioned above, one of the constructions in which a very sensitive variable resistance is necessary might be that of a temperature recorder such as shown in the application above mentioned, of which this is a division and there is shown in Figure 1 a casing 2 housing a recording mechanism as above described. The variregard to the frame by means of two insulating plates I26 and I28 at the opposite ends. Upon supporting members the exterior face of this tube is mounted a' cylinder I of Micarta or similar insulating material which is relatively thick. In the exterior surface of this member there is provided a spiral groove I32 which extends substantially the full length of the member thus forming between the grooves a spiral raised surface. A pair of parallel spaced conductors I34 and I36 are wound upon this surface and in similar spiral manner extend the full length of this insulating material. The opposite ends of one of these conductors is brought out through the insulated bushings I38 and I40 and the end of the other conductor is likewise brought out through the insulated bushing I 48, thus forming three terminals to be connected to a'circuit.

Rotatably mounted below and slightly to the rear of this tube is a long shaft I42 having axially extending teeth for substantially its full length, this shaft is trunnioned in the side walls of the frame I2 extending through the left hand wall to provide a smaller shaft section I44 upon which is mounted a spur gear I46. This engages a small driving pinion I48 mounted on a shaft 1 I50 of a reversible drive control motor I52.

Therefore, when the'motor I52 is energized, shaft I42 is rotated, and since the motor is reversible, this rotation may take place in either direction.

A short cylindrical sleeve member [54 having inwardly projecting teeth I55 on its inner surface, said teeth being of spiral configuration, is fitted over the insulatingMicarta tube I3 and is adapted to move axially along the same. Therefore, if the sleeve is rotated the projecting teeth which engage the spiral groove I32 in the micarta tube will cause the cylindrical member I54 to move along axially and assume the character of a travelling nut. Upon the outer surface of the cylindrical member I54 there is provided an in tegral set of spur gear teeth I58 which are adapted to mesh with the long axial teeth of the r0- tatable member I42 to cause the member I54 to rotate about the axis of the tube I24. Spaced I60 and I62 engage the opposite ends of the cylindrical member I54 and provide bearing means for the sleeve. These spaced members are held in proper position by spacer means I64 secured thereto by screws I66. Thus the member I54 may rotate within the v 7 frame so formed about the surface of the Micarta it does so causes axially movement of the sleeve along the tube. The ends of the members I60 and I62 project downwardly and are adapted to contact a cross bar I68 to prevent the whole assembly from turning around 3 the axis of the shaft when the gear l58 is driven.

Recording means such as a stylus I'M is provide on the carriage in this instance for recording purposes.

against a contact ball I36 forcin it down into contact with the upper surface 'oi two cent wires [34 and I35 thus bridging the gar between the two and causing a conductive connection at this point. As previously mentioned. one of the wires is utilized as a resistor in a measuring circuit and the other wire being ut conductor from th 'e' ore, if the ball or con- 1 s along the full length of the resistance wire we obtain an infinitely variable resistance and at the same time connect to of the resistance Wire a conductor for carrying current back to the apparatus. Thus, as'tn cylindrical member wi l rotates about the sleeve the contact ball I35 rolls spirally down the full length of the Wire to change the resistance as desired at the same time by bridging actio causes such balancing resistance point to c nested into the circuit without any contact i being carried by the movable or rotating oar Figure 3 shows a slightly modified form of travelling cylindrical means that in that in stance instead of the contact ball being held in place b a Micarta cup screw-threaded into an opening of the surface of the member if-.4, it is in this instance merely held in place by small insulating disc E88 which is spring bsod towa d the axis of the Micarta tube by a small spring lever I have thus provided infinitely adjustable resistance which can be connected into sensit' measuring circuit and there is no sudden step jumps in the value of resistance as would be provided in a wound resistor in which the contact member merely slides across from one turn of the coil to the other, but due to'the spiral drive, h a travelling contact or ball along the fl length. surface of the spirally wound wire as it is driven from one end to the other} It might be further added that this construction ha the added advantage that a long Wire may be spirally wound bet-we n relatively short end positions to provide a further increased variation in the resistance.

I claim:

1. In resistance means, a cylindrical member formed of insulating material having a spiral groove in its external surface, a pair of spaced conductors having resistance to current flow wound on the surface of the member between the grooved portions, means encircling a portion of the cylindrical member having projecting teeth that extend into the groove, means for movably and rotatably mounting the last named means whereby as he latter is rotated it will move axially along the surface of the cylindrical member, and conductive means mounted on the rotatable means to bridge the gap between the two con- I ductors at a point as the rotatable means moves along the member.

2. In resistance means, a stationed-v ovl -member f, 3,, 'rJAliclUal surface, a p of spaced conductors spirally wound on the surface of the member between the grooves, means rotatably mounted on themernbcr havine projecting portions extending into the groove to cause axial movement of the same, conducting means extending between the conductors mounted on the rotatable means to conduct current from one to: the other and wipe over the entire surfaces of both as the rotatable means is rotated.

S. In resistance means, a cylindrical insulating form having a spiral groove in its surface,a pair of conductors spirally wound in parallel relation on that section of the form between the grooves, a rotatable sleeve mounted around the form having projections extending into the grooves and a spring biased ball having a dial ieter greater than the distance between the conductors carried by the sleeve and rolling upon the surface of both conductors as the sleeve is rotated to interconnect the conductors at all times the sleeve moves axially of the form.

i. In resistance means, a stationary cylindrical member formed of insulating material and having spiral groove in its exterior surface, a pair of spaced parallel conductors spirally Wound on the surface of the member between the grooves, an insulating sleeve rotatably mounted on said menu bar hav' g internal projecting portions'extend into the groove to cause axial motion of the sl eve along the member as the sleeve rotates, said sleeve having an opening in surface in e gnment with the parallel conductors enclos d. ein, a cylindrical cap threaded into opening, a spring within said cap and a ball engaging the spring and adapted to roll on the sur faces of the parallel conductors to form a conductive path between the two as the sleeve progresses spirally along the cylindrical member.

ALBERT W. FISCHER. 

